I'm not a freshwater guy but I can tell you what I've found in my reef tanks. The overall population of colonista snails in both of my tanks seems to ebb and flow. Sometimes they reach plague levels and are everywhere. When this happens, I just manually remove all I can and the population just declines. Of course I've found that the population will typically decline regardless of what I do. With colonista's they don't really do any damage that I can tell. If your snail are damaging your other tank inhabitants the first step would be find out exactly what they are. Next figure out their food source and remove it if possible. All the while I'd be manually removing the dang things.
